1. Field of the Invention
The invention is related to the field of magnetic sensing devices and, in particular, to electrical lapping guides (ELG) made from tunneling magnetoresistive (TMR) material that are used in the fabrication of the magnetic sensing devices.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more recording heads (sometimes referred to as sliders) that include read elements and write elements. A suspension arm holds a recording head above a magnetic disk. When the magnetic disk rotates, an air flow generated by the rotation of the magnetic disk causes an air bearing surface (ABS) side of the recording head to ride a particular height above the magnetic disk. The height depends on the shape of the ABS. As the recording head rides on the air bearing, an actuator moves an actuator arm that is connected to the suspension arm to position the read element and the write element over selected tracks of the magnetic disk.
To read data from the magnetic disk, transitions on a track of the magnetic disk create magnetic fields. As the read element passes over the transitions, the magnetic fields of the transitions modulate the resistance of the read element. The change in resistance of the read element is detected by passing a sense current through the read element and then measuring the change in voltage across the read element. The resulting signal is used to recover the data encoded on the track of the magnetic disk.
Recording heads are typically manufactured on a substrate wafer that includes an array of recording heads. FIG. 1 illustrates a wafer 100 of recording heads in the prior art. The recording heads are arranged in rows on wafer 100. The dotted lines on FIG. 1 illustrate parting lines defining planes normal to the wafer plane, which will define the ABS of the recording heads. Wafer 100 is separated into rows of recording heads along the parting lines illustrated in FIG. 1. The rows are rough lapped from the ABS side of the recording heads to remove many microns of material to a desired rough lapping depth. The rows are then finally lapped to the final target forms using finer lapping plates. The final lapping process creates a desired stripe height of the read elements in the recording heads. The stripe height provides a desired magnetic characteristic for the read element in each recording head.
During the lapping process, a sense current may be passed through the read elements in the recording heads to monitor the lapping depth. The resistances of the read elements indicate the stripe height and may be used to control the depth of the lapping process. Lapping sensors called electrical lapping guides (ELG) may also be used to control the depth of the lapping process. If used, the ELGs are fabricated in the recording heads themselves or in the kerfs of wafer 100 between the recording heads.
FIG. 2 illustrates a row 200 of recording heads 202 that has been separated from wafer 100 in the prior art. The ABS of row 200 is the top surface 201 as shown in FIG. 2. Row 200 includes a plurality of recording heads 202. Each recording head 202 includes a read element 205, such as a magnetoresistive (MR) read element or a tunneling MR (TMR) read element. One or more ELGs 206 are also fabricated in the recording heads 202. The positioning of the ELGs 206 relative to the read elements 205 allows the ELGs 206 to control the lapping depth of row 200. As row 200 is lapped from the ABS 201, the resistances of ELGs 206 change. The resistances of ELGs 206 are related to the stripe height of read elements 205.
ELGs 206 may be formed from the same materials as read elements 205 in the same fabrication steps. For instance, one type of read element 205 is a TMR read element. A TMR read element, or magnetic tunnel junction (MTJ) read element, comprises first and second ferromagnetic layers separated by a thin, electrically insulating, tunnel barrier layer. The tunnel barrier layer is sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the ferromagnetic layers.
FIG. 3 illustrates an ELG 206 in row 200 formed from TMR material in the prior art. The ABS relative to ELG 206 is the plane of the paper of FIG. 3. By being formed from TMR material, ELG 206 includes a TMR stack 302 comprised of a first conductive (ferromagnetic) layer 311, a barrier layer 312, and a second conductive (ferromagnetic) layer 313. The layers 311-313 of ELG 206 are formed in the same deposition and lift-off steps as the layers of the read elements 205 (see FIG. 2). ELG 206 also includes leads 316-317 that connect to conductive pads (not shown) on the recording heads 202 (see FIG. 2). Leads 316-317 are deposited after layers 311-313 are deposited and contact the top of conductive layer 313. Leads 316-317 are connected in a current in plane (CIP) fashion for applying the sense current to ELG 206.
There are problems using TMR read elements or TMR ELGs as lapping guides. As is illustrated in FIG. 3, the barrier layer 312 separating the two conductive layers 311 and 313 is very thin, on the order of 10 Å. Because of the thinness of barrier layer 312, the lapping process (which is into the page in FIG. 3) can easily smear one of the conductive layers 311 across barrier layer 312 into the other conductive layer 313 causing a short between conductive layers 311 and 313. When conductive layers 311 and 313 are shorted across barrier layer 312, the resistance of ELG 206 can change dramatically. The changing resistance of ELG 206 unfortunately leads to ambiguity as to the desired stripe height and when to stop the lapping process.
To avoid this problem, a simple metallic material with low magnetoresistance, such as Ta or NiFe, has been used for ELGs instead of TMR material. However, there are other problems associated with using non-magnetic material for ELGs instead of TMR material. One problem is that there may be uncertainties in the definition of the back edge of the non-TMR ELGs relative to the TMR read element due to the variation in milling rates between the TMR read element and the ELG material. Another problem may be increased cost and increased cycle time. Additional fabrication steps are needed to form the non-TMR ELGs. For instance, during fabrication of a wafer, a full film of TMR material is deposited. A photoresist is then deposited to protect the TMR material of the TMR read elements. The wafer is then milled in the regions of the ELGs. The non-TMR material is then deposited to fill the holes milled for the ELGs. A liftoff process is then performed to lift off the ELG material and the photoresist. These additional steps of fabricating the non-TMR ELGs are undesirable.